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Related to September equinox: December solstice, June solstice

EQUINOX. The name given to two periods of the year when the days and nights are equal; that is, when the space of time between the rising and setting of the sun is one half of a natural day. Dig. 43, 13, 1, 8. Vide Day.

References in periodicals archive ?
This weekend brings the September equinox - so autumn is well on its way.
The September equinox occurs at 09:04 (or 9:04am) Coordinated Universal Time (UTC) on September 23, 2011.